The present disclosure relates to an automatic transmission that is mounted on a vehicle, and the like, and in particular, to an automatic transmission including a clutch that can engage or disengage the rotation transmission of two rotary members.
A wet multiple plate clutch is generally adopted for an automatic transmission, and in particular, for a multi-stage automatic transmission mounted on a vehicle, and the like (see Japanese Patent Application Publication No. 2008-115915). The wet multi-plate clutch includes, for example, a hydraulic servo disposed on an outer peripheral side of a central shaft disposed at a center of the automatic transmission. When engaging such a clutch, an engagement pressure is supplied to a hydraulic oil chamber through an oil passage, which passes through the interior of the central shaft, and a piston is pressed and driven in an axial direction to press a plurality of friction plates and engage the friction plates, thereby engaging the power transmission of two rotary members.
When disengaging such a clutch, the engagement pressure supplied to the hydraulic oil chamber is lowered (engagement pressure is removed from the oil passage passing through the interior of the central shaft), and the piston is pressed and moved to the opposite side in the axial direction mainly by an urging force of a return spring. In this case, however, a pressure (centrifugal oil pressure) caused by the centrifugal force is generated in the hydraulic oil of the hydraulic oil chamber since the hydraulic servo is in a rotating state in most cases, and it is often difficult to disengage the clutch with only the urging force of the return spring. Thus, a cancel oil chamber having the same pressure receiving area as that of the hydraulic oil chamber is provided and the cancel oil chamber is filled with oil to cancel the centrifugal oil pressure generated in the piston member, thereby making the axial movement of the piston by the return spring smooth and achieving the disengagement of the clutch.